Equilibrium

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Unit 5

36 Terms

1
What is equilibrium
Equilibrium is reached when rate of forward reaction = rate of reverse reaction, solution is balanced

Macroscopically: nothing happens

Microscopically: reactants are converted to products and products are converted to reactants
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2
Why is equilibrium said to be dynamic
Because of the continual conversion of reactant to product
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3
Exothermic reactants are hard to reverse if…
the change in heat is very large. It means that the Eareverse is also large.
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4
Equilibrium must establish in what
A closed system
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5
Why do some reactants have a %yield of less than %100
because reverse reactions can take place after products are formed
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6
Example of Dynamic Equilibrium: Radioactive NaI\* in saturated NaI solution
Size of lump does not change (macroscopically) but overtime, solution becomes radioactive (microscopically). This indicates that NaI\* is dissociating and ions are moving out into solution. The ions from the NaI solution are crystalizing on the surface of the lump. So, the rate of dissociation (forward) and crystallization (reverse) are equal and it is at equilibrium.
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7
Le Chatlilier’s Prinicple
If you disturb an equilibrium, it will shift to counteract the disturbance
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8
Why will the disturbed equilibrium never reach its initial conditions?
because an equilibrium can only counteract up to %10. a new equilibrium will eventually establish
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9
How to optimize the amount of product at equilibrium
flood reaction vessel while continuously removing product
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10
Increasing the concentration of reactant or product
shifts equilibrium away from increase
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11
Decreasing the concentration of reactant or product
shifts equilibrium towards decrease
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12
As volume is … pressure is …
decreased, increased (inversely proportional)
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13
An increase in pressure favours which direction
the direction with fewer moles of gas
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14
what effect does pressure have in a reaction with the same amount of reactant and product moles
pressure has no effect
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15
N2O4 (g)
the formation of N2O4 will be favoured since it has less moles. the reverse reaction is favoured
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16
What is the equilibrium constant dependent on?
temperature
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17
Endothermic reaction. Adding heat and removing heat
ΔH>0, heat is a reactant. Adding heat favours the forward reaction and cooling favours the reverse reaction
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18
Exothermic reaction. Adding heat and removing heat
ΔH
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19
why does a catalyst not affect the equilibrium
because it decreases the Ea forward and the Ea reverse the same amount
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20
Equilibrium constant (k)
kc = \[products\]/\[reactants\]
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21
kc
based on the molarities of reactants and products at equilibrium

unitless
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22
large k vs small k
large k: more products present at equilibrium

small k: less products present at equilibrium
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23
if k > 1
products dominate at equilibrium and equilibrium lies to the right
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24
if k < 1
reactants dominate at equilibrium and equilibrium lies to the left
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25
k of reaction in opposite direction
the reciprocal of the k in the other direction
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26
Homogeneous Equilibria
when all reactants and products are in one state
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27
Heterogeneous Equilibria
when one or more reactants or products are in a different state
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28
Why do we ignore the concentrations of pure liquids, solvents and pure solids in equilibrium constant expressions
density and molar mass are not variables and we can’t find the concentration of something that isn’t a solution
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29
To predict the direction of reaction
compare Q and K
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30
Reaction not at equilibrium (Q)
Q = \[products\] / \[reactants\]

molarities at any time
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31
if Q > k
reverse reaction occurs to reach equilibrium

shifts to left
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32
if Q < k
forward reaction occurs to reach equilibrium

shifts to right
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33
for Q to be large…
must have lots of product
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34
for Q to be small…
must have lots of reactants
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35
if Q = k
system is at equilibrium
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36
The hundreds rule
initial concentrations / kc

if value is greater than 100, can ignore any x value added or subtracted
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